Mist spinning



Dec. 10, 1968 5.1. CARTER ETAL 3,415,922

uls'r SPINNING Filed July 2, 1965 INVENTORS PAUL R. cox, JR EARNESTCARTE'R WILLIAM .LANIER ATTO E United States Patent 3,415,922 MISTSPINNING Ernest P. Carter, Durham, and Paul R. Cox, Jr., Cary,

N.C., and William E. Lanier, Hartselle, Ala., assignors to MonsantoCompany, St. Louis, Mo., a corporation of Delaware Filed July 2, 1965,Ser. No. 469,103 6 Claims. (Cl. 264--1.76)

ABSTRACT OF THE DISCLOSURE A process for removing solvent from asolution of filament-forming material and solvent and for collecting theremoved solvent includes the contacting of the solution while in anextruded filament-form with an atomized liquid which condenses on thefilament-forms to diffuse the solvent therefrom, the stripping of thecondensate from the filament-forms and collecting of the strippedcondensate.

The present invention relates to the production of textile filaments.More particularly, this invention relates to an improved spinningprocess for producing filaments wherein a mist coagulant is utilized toform better quality filaments from a solution of fiber-forming materialsdissolved in a suitable organic solvent.

In the production of filamments by the typical wetspinning processes,the solution of fiber-forming materials is extruded into a coagulatingbath which contains a liquid coagulant for the fiber-forming materials.The filaments are formed as the solvent diffuses out into thecoagulation bath. This diffusion is generally accompanied by thepenetration of the coagulating bath liquid into the filament. Therefore,a clean bath must be maintained to prevent contamination of thefilaments. One of the major problems with preparing filaments by theseprocesses is the fragility of the newly formed extrusions. Because ofthis initial fragileness, the filaments may be damaged easily andvarious precautions are necessary if good quality filaments are to beobtained. For example, the spinning speed must be reduced in order toavoid breaks and damage to the fragile filaments because of the densityof the liquid coagulating bath. Also, the coagulating bath must beregulated closely to insure that the extracted solvent is removed whilemaintaining minimum turbulence in the bath to avoid contaminating ordamaging the newly formed filaments. Thus, a recirculating systemcapable of maintaining accurately controlled conditions is essential.

Several techniques have been devised in attempts to overcome theproblems experienced with the known wetspinning processes. In someinstances, it has been rec ommended that spinning tubes be used tominimize turbulence in the bath flow. Others have recommended that thebath flow at the same rate as the extrusion rate so that no drag ortension will be exerted on the newly formed filaments. Perhaps thesemethods tend to reduce, to some extent, the problems imposed by theliquid coagulating bath, but none of them effectively eliminate all suchproblems because of the inherent physical conditions established by thebath itself. Furthermore, the liquid coagulating bath must be maintainedat elevated temperatures which cause slight color formation of somepolymers.

Although the problems experienced in wet spinning and dry spinningprocesses are not similar, there are however, some inherentdisadvantages encountered with the typical dry-spinning processes. Theseinclude the limitations such as the low number of ends and the smalldeniers which the spinning processes must be limited in order to avoidfiber coalesence or married fibers. Also, the elevated tem- 3,415,922Patented Dec. 10, 1968 peratures employed to facilitate'drying andsolvent removal cause yellowing of acrylic polymers.

It is an object of fthe present invention to provide an improvedspinning process wherein the filaments are coagulated by a mistcoagulating medium.

Another object of the present invention is to provide an improvedspinning process wherein the newly formed filaments are not contaminatedas heretofore by impur ities that normally occur in the liquid spinbaths which collect on the filaments.

A further object of the invention is tot provide a process whichfacilitates faster spinning rates and improved fiber qualities.

Still another object of the invention is to provide a process forcoagulating filament-forming materials with a mist coagulant atapproximately ambient temperature to prevent color formation normallycaused by elevated temperatures.

Yet another object of the invention is to provide a process whichfacilitates uniform solvent removal to produce cleaner fibers.

Another object of the invention is "to provide an improved processwherein the coagulating zone is enclosed and free of collectedimpurities.

Other objects and advantages of the present invention will becomeapparent from the detailed description and drawing.

The objects of this invention have been accomplished by extruding asolution of filament-forming polymers through a spinneret located in agenerally enclosed chamber filled with a suitable coagulant introducedtherein as a mist or fine spray which diffuses or causes a chemicalreaction to remove the polymer solvent from the extruded solution andcoagulates the remaining filament-forming polymers to form filamentsthat are withdrawn from the mist-filled chamber and then advancedthrough successive washing, stretching, and drying operations.Subsequently, the mist spinning process contemplated by the presentinvention is distinguishable from the known spinning processes by themanner in which coagulation is achieved. Instead of extruding thefilaments into a liquid bath or heated chamber to accomplishcoagulation, the extrusion is made into an enclosure where the coagulantemployed is in the form of a fine mist at approximately 25 C. whichinstantly saturates the emerging extrusions and transports the diffusedsolvent out of contact therewith to produce clean filaments having lowersolvent content that must be removed later by washing than regularwet-spun filaments. Thus, the solvent is uniformly extracted in asubstantialy frictionless coagulating environment at ambienttemperatures wherein increased spinning speeds can be employed toproduce higher quality fibers more cheaply than by normal wet-spinningprocesses known heretofore.

By mist coagulant, as employed herein, is meant a liquid reduced toultra-fine particles by a pressurized fluid which is a nonsolvent forthe fiber-forming polymers but a solvent for the polymer solvent.

The present invention will be more clearly understood by reference tothe accompanying drawing in which a single figure illustrates a sideelevation, partly in crosssection, of suitable apparatus foraccomplishing the objects set forth.

Referring specifically to the individual elements and their arrangementas illustrated by the drawing, there is shown a spinneret or jet 10located in a chamber 12. The spinneret is positioned for horizontalextrusion of filament-forming materials supplied through rounder arm 14from a source, not shown. A conventional spray nozzle 16 is disposed inthe upper portion of chamber 12 for introducing a mist or spray 18 intothe area enclosed by the chamber to produce a vaporized atmosphere whichfunctions as a coagulating zone 20. The mist or spray is vaporized bypressurized gas such as air, and may be comprised of water, but amixture of water and a suitable solvent for the filament-formingmaterials has been found to be preferable. As the extrusions emerge fromthe spinneret 10, they are coagulated by the mist or spray coagulant 18to form a ribbon of filaments 22. The filaments are withdrawn from thechamber 12 through a group of horizontally aligned bars 24 to strip orremove excessive amounts of water and solvent condensate from thefilamentary structures. A drain 26 is provided for removing the mixtureof water and solvents from the chamber 12 thereby preventingcontamination of the filaments with the diffused solvents and removingdeleterious drag normally imposed by a liquid bath.

Although the filaments prepared in accordance with the present inventionare cleaner than filaments prepared by typical wet-spinning processes,the solvent is not always entirely diffused or reacted from thefilaments by the mist coagulant 18. Therefore, it is desirable toadvance the withdrawn filaments through a wash bath to remove anyremaining solvent.

The invention will be further illustrated but is not intended to belimited by the following examples which define parts and percentages byweight unless otherwise specified. The tests for color indicative ofapproaching whiteness used throughout the examples consist ofmeasurements of brightness and purity as calculated from the tristimulusvalues determined on a General Electric Spectrophotometer in accordancewith the methods recommended by the Standard Observer and CoordinateSystem of the International Commission on Illumination as fully setforth in the Handbook of Colorimetry published by the Technology Press,Massachusetts Institute of Technology 1935. The test results are givenin figures which indicate a greater whiteness or purity as they decreasetowards zero.

Example I A slurry of 250 grams of a copolymer of 93 percentacrylonitrile-7 percent vinylacetate in 750 grams of dimet-hylacetamidewas prepared by chilling the dimethylacetamide to 10 0., adding thecopolymer to the chilled slurry and mixing the slurry for 10 minutes.The slurry was then heated to 75 C. with continuous agitation. Heatingand stirring was continued at this temperature for two hours to form ahomogeneous solution. The polymer solution was extruded through alO-hole, 3.5-mil diameter spinneret into a coagulation bath containing55 percent dimethylacetamide and 45 percent water at a temperature of 55C. The solution was converted into fiber in the coagulation bath andremoved from the bath, after an immersion of 1.5 inches, by advancingrolls. The fiber was next passed through a boiling water bath where itwas stretched 5.0 times, the stretch being imparted by another set ofadvancing rolls traveling at a faster speed than the first set ofadvancing rolls. The oriented fibers were then passed through an aqueousbath where a conventional antistatic finish was applied. The fiber wasthen dried by a final set of rolls, traveling at 71 f.p.m., which weresteam heated to 105 C. The dried fiber had a denier per filament of12.5, an elongation of 17 percent, and a tenacity of 2.9 grams perdenier. The brightness, purity, and dominant wave length of this fiberwere 88.7, 7.9, and 574 m respectively.

Example II The procedure followed in Example I was repeated with theexception that the spinneret was positioned 0.25 inch above the spinbath, the fibers extruded vertical to the bath surface, and passedaround a ceramic guide to permit removal from the bath after a totalimmersion of 1.5 inches. The denier per filament was 12.54, elongationwas 19 percent and the tenacity was 3.10 grams per denier.

The brightness, purity and dominant wave length were 87.8, 7.5, and 574III/.0, respectively.

Example III The procedure followed in Example I was repeated with theexception that the bath employed in the two previous examples wasreplaced with a chamber into which was sprayed a coagulating mist whichconsisted of a mixture of air and water at room temperature (25 C.). Thenozzle employed gave a hollow cone spray from a 0.028- inch orificediameter and at 25 psig. delivered 2.4 gallons of water per hour at roomtemperature. The nozzle was located approximately 2 inches below and 0.5inch in front of the spinneret. The chamber employed was 24 inches wide,25 inches deep, and 30 inc-hes in height and was constructed ofPlexiglas with three sides and a top to permit viewing of the spinningprocess and with one side open to permit removal of the fibers. Thechamber was set in a stainless steel pan fitted with a drain to collectany mist condensate which formed during spinning. The fiber, on passingfrom the open end of the mist chamber, was passed over a ceramic guidewhich stripped condensate from the fibers. The fiber had a denier perfilament of 15.29, a tenacity of 2.93 grams per denier and an elongationof 15 percent. The brightness, purity, and dominate wave length were87.8, 6.9, and 573 III/1., respectively. A skin core elfect was observedin the fiber cross-section.

Example IV The procedure followed in Example III was repeated with theexception that the mist employed was a 50:50 mixture of water anddimethylacetamide. The fibers obtained were identical to those obtainedin Example III with the exception that the skin-core elfect was reducedand the fibers were more uniform in cross-section.

Example V The procedure followed in Example I was repeated with theexception that the maximum continuous spinning speed, as measured at thedrier rolls, was established as 337 f.p.m. This speed is the speed whichcan be maintained continuously without breaking a filament. The speed isdetermined by successively increasing the speed of each roll until afilament breaks and then setting the speed at percent of the breakingspeed.

Example VI The experiment described in Example V was repeated with theexception that the wet spinning coagulation bath was replaced with themist spinning apparatus described in Example III. The maximum continuousspinning speed was 420 f.p.m., an increase of 25.4 percent over thespeeds obtained in Example V.

Example VII The procedure described in Example III was repeated with theexception that the concentration of polymer in solution was decreasedfrom 25 percent by weight to 20 percent by weight. The spinning speedwas increased to 220 f.p.m. at the drier roll. The fiber obtained had adenier per filament of 4.14; tenacity of 2.9 grams per denier and anelongation of 10.0 percent.

Example VIII The procedure described in Example III was repeated withthe exception that a SOO-hole, 3-mil diameter spinneret with the holesrandomly distributed over the spinnerets l-inch face was employed. Itwas observed that with a single jet for mist formation coagulation wasincomplete and it was necessary to install a second jet, identical tothe first but located above the spinneret in order to obtain continuous,trouble-free spinning. The fibers obtained with the dual jet system wereequivalent to those obtained in Example III.

5 Example IX A 30 percent by weight solution of poly(vinyltrifiuoroacetate) in acetone was prepared by adding 300 grams ofthe polymer, prepared as described in the copending application Ser. No.358,243 filed Apr. 8, 1964, to 700 grams of acetone which had beenpreviously chilled to C., slurrying the mixture until the polymer wasthoroughly wet and then allowing the mixture to warm to roomtemperature. Agitation was continued for two hours to assure that thepolymer was completely dissolved. The solution was spun into fiber asdescribed in Example [I I with the exception that the finish bath wasreplaced with a 37 percent by weight solution of ammonium hydroxide at26 C. The poly(vinyltrifluoroacetate) was continuously hydrolyzed in theammonium hydroxide bath to poly(vinyl alcohol). The fibers obtained wereclear, flexible and had a denier per filament of 11.9, tenacity of 4.9grams per denier, and an elongation of 22 percent.

Example X A solution containing 100 grams of polyOvinyl chloride) and 60grams of N,N-dimethyl lauramide in 240 grams of dimethylformamide wasprepared by first dissolving the amide in the solvent, slurrying thismixture at C. with the poly(vinyl chloride) and then heating the mixtureto 85 C. for 30 minutes. The clear viscous solution was then extrudedthrough a -hole, S-mil diameter spinneret into a mist chamber, such asthat described in Example III, into a mist of 10 percent by volumedimethylformamide and 90 percent by volume water. The mist formingnozzle was positioned 8 inches in front of and 2 inches below thespinneret. The remaining spinning conditions were identical to thoseemployed in Example III. The fibers had a denier per filament of 736, atenacity of 0.14 gram per denier, an elongation of 231 percent, atenacity at 50 percent extension of 0.03 gram per denier, a tensilerecovery after stretching and releasing tension of 94.8 percent, and astress decay of 12.0 percent on the second extension.

Example Xl A solution of 35 percent by weight nylon 6 in formic acid wasprepared by heating the polymer having a relative viscosity of 72, at 50C. for two hours with gentle stirring. The clear homogeneous solutionwhich resulted was spun according to the procedure described in ExampleIII with the exception that a 10-hole, 2-mil diameter spinneret wasemployed and the mist was generated by spraying a 10 percent by weightsodium hydroxide solution through the mist forming orifice. The fibersobtained were clear translucent fibers having a denier per filament of3.5, a tenacity of 3.4 grams per denier, and an elongation of 28percent.

Example XII A solution of an isocyanate modified dihydroxy elastomerwith a viscosity of approximately 30,000 cps., prepared as described incopending application Ser. No. 369,- 019, was spun by the processdescribed in Example III to produce elastomeric fibers having improvedcolor. By carrying out the coagulation in a mist atmosphere thedeleterious drag of spinning solutions is eliminated and the problemsassociated with broken filaments is removed.

Example XIII A slurry of 2,500 grams of a copolymer of 93 percentacrylonitrile-7 percent vinylacetate in 7.50 grams of dimethylacetamidewas prepared by chilling the dimethylacetamide to -l0 C., adding thecopolymer and mixing the chilled slurry for 30 minutes. The slunry wasthen heated to 65 C. and mixed for two hours to form a clear homogeneoussolution. Attempts were then made to dry spin the solution into fibersusing the apparatus described in the patent US. 2,636,217 to W. H.Hammond et al.,

using a 10-hole, 3-mil diameter spinneret. At pump speeds calculated toproduce a 12.5 denier per filament fiber the filaments contacted eachother before the solidification process could be completed to produce anunsatisfactory bundle of married filaments.

Example XIV The experiment described in Example XIII was repeated withthe exception that a fine mist of Water was introduced into the tower atroom temperature. The mist was produced by introducing nitrogen at 25p.s.i.g. and water at 2.4 gallons per hour into a hollow cone spray witha 0.028-inch orifice diameter. After advancing a distance of less thanone foot from the spinneret face the fibers were sufliciently solidifiedto permit their removal from the apparatus for further processing. Theapparatus was modified to permit the removal of the fiber after one footof vertical travel and the arrangements for heating the apparatus wereeliminated. The fibers were passed over a ceramic guide and advancedhorizontally to advancing rolls and then stretched 5 times: in a boilingwater bath by a second set of rolls. The fibers were thoroughly Washedwith 60 C. water on the second rolls, passed through an aqueous finishedbath containing an antistatic finish agent, dried on a final set ofsteam heated rolls at C., and collected at 68 f.p.m. on a conventionaltake-up machine. The collected fibers were free of married filaments andafter exposure to boiling water for 5 minutes had a denier per filamentof 17.4, a tenacity of 2.57 grams per denier and an elongation of 27.6percent.

Example XV The procedure described in Example XIV was repeated with theexceptions that a SOD-hole, 3-mil diameter spinneret was used and threenozzles located in a plane 0.5 inch below the spinneret at intervals andat a distance of 2 inches from the extruded fibers were employed. Thepumping rate was increased 50 times to accommodate the additional numberof holes in the spinneret. The properties of the spun fiber wereessentially identical to those obtained in Example XIV.

Example XVI The procedure described in Example XIV was repeated With theexception that the copolymer employed in Example XIV was replaced with ablend. of 88 percent by weight of a copolymer of 97 percentacrlylonitrile and 3 percent vinyl acetate with 12 percent by weight ofa copolymer of 50 percent acrylontrile and 50 percent 2-methyl-S-vinylpyridine and the concentration of the sol.- vent wasincreased to 82 percent by weight. The fibers obtained after exposure toboiling water for 5 minutes had a denier per filament of 15.4, atenacity of 1.9 gram per denier, and an elongation of 39 percent.

Example XVII A solution of approximately 23 percent isocyanate modifieddihydroxy elastomer polymer, such as the polymer described in copendingapplication Ser. No. 369,019 filed May 20, 1964, mixed indimethylformamide solvent was spun by the process described in ExampleXIV to give married elastomeric fibers having improved color and by amore economical process. By either increasing the number of mist formingnozzles or by varying the point of removal from the spinning apparatusit was found that unmarried fibers could be produced. Also, by employinglower spinning temperatures, a product having improved color wasobtained.

From the data set forth in the foregoing examples, it is apparent thatfilaments spun in accordance with the present invention have severalimproved qualities over filaments spun in accordance with the procedureof EX- amples I and II which are typical of the conventionalwet-spinning processes and Example XIII which represents a typicaldry-spinning process. The spinning speeds for the wet-spinning processesare directly related to the amount of drag imposed on the newly formedfilaments. Therefore, by accomplishing the fiber coagulation in a mistatmosphere, the deleterious drag of spinning solutions normallyencountered will be eliminated and the accompanying problems associatedwith broken filaments will be removed. In addition to faster spinningspeeds, the mist atmosphere facilitates the preparation of fibers havingimproved whiteness. For example, where the spinneret is submerged in aliquid bath, the temperature must be elevated somewhat to avoid loweringthe temperature of the spinneret, which changes the viscosity of thespinning solution. Similarly, in the dry spinning processes elevatedtemperatures are employed to facilitate fiber formation and solventremoval. The elevated temperatures tend to cause color formation of somepolymers such as the acrylics unless special precautions are observed.Since the mist does not remove a substantial amount of heat from thespinneret, and the solvent is removed by said mist, the coagulatingmedium can be maintained at a much lower temperature while optimumspinning conditions are observed. In addition to the improved fiberqualities, coagulation is accomplished in a hooded area which reducessolvent evaporation and thereby reduces costs.

Generally, this process is applicable to the spinning of a broad rangeof synthetic fiber-forming polymers and polymer blends which may besolution spun by methods Well known in the art. Included among thesesynthetic materials are acrylic polymers, notably homopolymers andinterpolymers of acrylonitrile. The acrylonitrile polymers containing atleast 85 percent of acr ylonitrile, interpolymerized with one or moreethylenically unsaturated monomers copolymerized therewith, such asmethyl acrylate, acrylic acid, methacrylic acid, vinyl acetate, vinylpyridine, vinyl chloride, vinyl bromide, styrene and the like areparticularly preferred. Other fiber-forming polymers such as polyamides,polyesters, polyurethanes, vinyl polymers and the like may be solutionspun by the process of this invention.

The particular solvent employed to dissolve the polymer will, of course,depend on the identity of the polymer in each particular instance as iswell known in the art. Where the above-described polymers of:acrylonitrile are spun according to this invention, it is mostdesirable to employ organic polar solvents such as dimethylformamide,dimethylacetamide, dimethyl sulfoxide, butyrolactone, ethylenecarbonate, propylene carbonate, and the like. However, other knownsolvents such as aqueous salt solutions may likewise be employed for theacrylic polymers.

It has been found that conditions in the spinning chamber are notgenerally critical except that the mist or spray must be reduced toultra-fine particles which are present in abundance to coagulate thefiber-forming polymers. Thus, the particles must be small enough toimpinge upon the freshly extruded threadlines without breaking the finedenier filaments. Also, as described elsewhere herein, it has been foundto be particularly advantageous to maintain the temperature level in thespinningchamber at approximately ambient temperature when spinningacrylonitrile, polyurethane, etc. to prevent yellowing of the fibers.

The foregoing detailed description has been given for clearness ofunderstanding only, and unnecessary limitations are not to be construedtherefrom. The invention is not to be limited to the exact details shownand described since obvious modifications will occur to those skilled inthe art, and any departure from the description herein that conforms tothe present invention is intended to be included within the scope of theclaims.

What is claimed:

1. A process for removing solvent from a solvent comprised of apolymeric filament-forming material and a solvent for said polymericmaterial and for collecting said removed solvent, comprising:

(a) extruding said solution into an enclosed chamber in filament-f0rm,having a plurality of openings, said filament-forms being guided along apath through said chamber and out a first one of said openings;

(b) injecting into said chamber through a second one of said openings,said atomized liquid being a solvent for said polymeric material solventand being inert to said polymeric material, said atomized liquidcontacting said filament-forms and condensing thereon whereupon portionsof said polymeric material solvent is diffused from said filament-formsto coagulate the same;

(0) stripping said condensate from said coagulated filament-forms, saidcondensate being comprised of said atomized liquid and said polymericmaterial solvent; and

(d) collecting said stripped condensate in said chamber at a pointremoved from said filament-forms path.

2. The process of claim 1 wherein said atomized liquid is Water.

3. The process of claim 1 wherein said atomized liquid is comprised ofwater and an organic polar solvent for said filament-forming material.

4. The process of claim 1 wherein said atomized liquid is comprised ofan aqueous salt solution.

5. The process of claim 1 wherein said path along which saidfilament-forms are guided is horizontally disposed in said chamber.

6. The process of claim 1 wherein said collected condensate is removedfrom said chamber by means of a drain forming a third one of saidchamber openings.

References Cited UNITED STATES PATENTS 1,583,475 5/1926 Lahousse 264167X 2,354,744 8/ 1944 Dreyfus.

2,425,782 8/ 1947 Bludworth et al. 264203 2,463,676 3/1949 Bludworth etal. 264--203 2,948,584 8/1960 Euler et al. 264-206 2,975,022 3/1961Euler et al. 264-206 JULIUS FROME, Primary Examiner.

J. H. WOO, Assistant Examiner.

US. Cl. X.R. 264-344, 203, 205

